1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a belt in which at least a portion of the compression layer thereof is formed from a rubber composite material exhibiting excellent wear and running characteristics at both high and low temperatures in both dry and damp environments.
2. Background Art
V-ribbed belts have many features which have made them highly useful in several diverse environments, including, for example: the automotive and general purpose vehicle industries; the agricultural industry for equipment such as tractors; the electrical industry for a wide range of equipment, etc. Most notable of the desirable features of the V-ribbed belt is the inherent flexibility that it has. It is generally thinner than a single rib V-belt, resulting in minimal bending stresses in operation. This flexibility permits the V-ribbed belt to be incorporated into a system with very small diameter pulleys. The advantage of this is that the overall system into which the V-ribbed belt is incorporated may be made very compact. The use of V-ribbed belts also accounts for a substantial energy savings in the systems in which they are operated. A further advantage of the V-ribbed belt is that the individual ribs are not required to penetrate a complementary pulley groove as deeply as a conventional single rib V-belt. This results in less friction development upon the ribs entering and withdrawing from the grooves and, in addition to affording energy savings, results in reduced belt wear and ultimately longer belt life.
While the V-ribbed belt has all of the above advantages, such belts also have some inherent limitations. There is a tendency of the belt to slip when an excessive load is driven by the belt. Further, any variation in loading on the system may produce the same slippage. This slippage over time removes a substantial amount of the rubber from the ribs and may cause cracks to develop therein with resulting shortening of the life of the belt.
Typically, the V-ribbed belt consists of an inner compression section/layer and an outer tension section/layer. Between the compression and tension sections/layers are typically included a plurality of longitudinal tensile cords which are embedded in parallel relationship in an adhesive rubber layer. At least part of the compression section is defined by longitudinally extending, laterally spaced, V-shaped ribs. It is known in the belt art to embed short fibers in the compression rubber layer. Typically these fibers are included in amounts between 20 to 40 parts by weight of fiber to 100 parts by weight of matrix rubber.
A typical rubber used for general purpose application is chloroprene rubber (CR). It is known in the art to improve durability under severe conditions by using epichlorohydrin rubber (CHR), chlorosulfonated polyethylene rubber (CSM), ethylene-propylene-diene rubber (EPDM), etc. These rubbers exhibit excellent resistance to high temperatures.
However, there are various drawbacks with each of these materials which have been contended with in the prior art. Epichlorohydrin rubber (CHR) operates poorly, and has insufficient flexibility, in cold environments. Chlorosulfonated polyethylene rubber (CSM) generates a substantial amount of internal heat during operation and has poor resistance to cold temperatures and oil. Ethylene-propylene-diene rubber (EPDM) is also detrimentally affected by oil.